Obtenção de insumos quimicos e farmaceuticos a partir da lignina hidrolitica de eucalipto

AUTOR(ES)
DATA DE PUBLICAÇÃO

1991

RESUMO

The conversion of hydrolytic eucalyptus lignin by hydrogenolysis, alkaline hydrolysis and oxidation was studied with the objective to produce low molecular weight substances. The lignin was obtained by acid hydrolysis of eucalyptus wood at Coalbra Company and at the Foundation of Industrial Technology (FTI) in Lorena. The lignin was submitted to hydrogenolysis with sodium formate in water under pressure, using microwave and ultrasound irradiations for pretreatment. The reactions did not give good oil yields even after pretreatment, reaching a maximum of 30%. Alkaline hydrolysis with sodium hydroxide in a dioxane/water mixture was performed under an argon atmosphere, varying the solvent composition, the reaction pressure and the solvent/lignin ratio. We found that the oil yield increased if pressures between 40 and 60 bar were used. A conversion better than 70% and an oil yield of approximately 50% was obtained when a solvent/lignin ratio of 40:1 was used. Among the reactions products, guaiacol, phenol and 2,6-dimethoxyphenol were identified with 5.9%, 1.6% and 3.4% yields with respect to the starting lignin. The mechanism is discussed based on the products obtained. The oxidation reactions were initially performed in water under air utilizing cobalt(III) acetylacetonate as a catalyst. The lignin was then converted in acetic acid with pure oxygen and the same cobalt catalyst. After optimization of the oxidation reactions, cobalt(II) acetate was used as a catalyst and sodium bromide as a promoter. In these reactions it was verified that water reduced the oil yield by hindering radical reactions. In acetic acid an oil yield of 37% and a conversion of 70% was obtained. On the other hand, the oxygen pressure and the temperature have to be well controlled as explosions may occur. Using cobalt(II) acetate the results improved approximately 10% and the reactions performed at 210°C gave better oil yields than that at 240°C. Sodium bromide acts as a promoter of the oxidation. Using a quantity of sodium bromide five times higher than that of the catalyst, we achieved a conversion of 75.6% and a oil yield of 67.2%, which we consider excellent. The GC-MS analysis af the volatiles showed ten principal compounds which have not yet been identified as their mass spectra do not show the molecular ion.

ASSUNTO(S)

quimica da biomassa lignina

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